Combustion in diesel engines is facilitated via compressing air-fuel mixtures within engine cylinders. As an air-fuel mixture is compressed, temperature and pressure within the cylinder increases such that the air-fuel mixture ignites without an externally supplied ignition source such as a spark plug. Ignition of the air-fuel mixture releases heat and increases temperature and pressure within the cylinder. Depending on conditions, the engine combustion may increase engine noise and reduce driver satisfaction.
One approach to address combustion noise is to provide pilot fuel injections during a cylinder cycle. The pilot fuel injections are introduced to a cylinder in advance of the main fuel injection pulse. By adjusting the number and timing of pilot fuel injections, it may be possible to change the ignition time and rate of heat release during combustion of an air-fuel mixture so as to reduce combustion noise and improve driver satisfaction. However, a fixed number of pilot fuel injections may not provide desirable engine combustion noise and heat release characteristics over an engine operating range. Rather, it may be desirable to vary the number of pilot fuel injections with engine operating conditions. Nevertheless, if a number of pilot fuel injections is changed and pressure of the injected fuel is not at a desired level when the number of fuel injections changes, engine noise may not be within a desired range.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method for fueling an engine, comprising: transitioning from supplying fuel to a cylinder based on a first relationship between fuel pressure and a number of pilot fuel injections to supplying fuel to the cylinder based on a second relationship between fuel pressure and the number of pilot fuel injections, the transitioning in response to a first condition when a control parameter is increasing.
By changing between different fuel pressure controls tables as a number of pilot fuel injections are changed, it may be possible to provide improved fuel pressure control for fuel injectors when a number of pilot fuel injections are changed in response to a change in engine operating conditions. For example, a first fuel rail pressure control table may be the basis for controlling fuel rail fuel pressure when a single pilot fuel injection pulse is provided to a cylinder. On the other hand, a second fuel rail pressure control table may be the basis for controlling fuel rail fuel pressure when two pilot fuel injection pulses are provided to the cylinder. Thus, fuel rail pressure may be adjusted by jumping between two fuel rail fuel pressure tables in response to a number of pilot fuel injections supplied to a cylinder. In this way, fuel pressure may be quickly changed as a number of pilot fuel injections change so that fuel pressure lag between different operating conditions may be reduced.
The present description may provide several advantages. Specifically, the approach may useful for transitioning between fuel injection modes. In particular, the approach may reduce engine emissions such as HC, NOx, and CO by allowing more rapid fuel pressure changes between conditions where different numbers of pilot fuel injections are supplied by a fuel injector. Further, the approach may reduce an amount of time to calibrate an engine because calibrating for gradual transitions between fuel injection mode changes may be avoided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.